The present invention relates to arrangements to make gas fired water heaters safer for use.
The most commonly used gas-fired water heater is the storage type, generally comprising an assembly of a water tank, a main gas burner to provide heat to the tank, a standing pilot burner to initiate the main burner on demand, an air inlet adjacent the burner near the base of the jacket, an exhaust flue and a jacket to cover these components. Another type of gas-fired water heater is the instantaneous type which has a water flow path through a heat exchanger heated, again, by a main burner initiated from a pilot burner flame. For convenience, the following description is in terms of storage type water heaters but the present invention is not limited to this type. Thus, reference to xe2x80x9cwater container,xe2x80x9d xe2x80x9cwater containment and flow means,xe2x80x9d xe2x80x9cmeans for storing or containing waterxe2x80x9d and similar such terms includes water tanks, reservoirs, bladders, bags and the like in gas-fired water heaters of the storage type and water flow paths such as pipes, tubes, conduits, heat exchangers and the like in gas-fired water heaters of the instantaneous type.
A particular difficulty with many locations for water heaters is that they are also used for storage of other equipment such as lawn mowers, trimmers, snow blowers and the like. It is a common procedure for such machinery to be refueled in such locations.
There have been a number of reported instances of spilled gasoline and associated fumes being accidently ignited. There are many available ignition sources, such as refrigerators, running engines, electric motors, electric light switches and the like. However, gas water heaters have sometimes been suspected because they often have a pilot flame.
Any vapors from spilt or escaping flammable liquid or gaseous substances in a space in which an ignition source is present, provides a potential for ignition. xe2x80x9cFumes,xe2x80x9d xe2x80x9cextraneous gasesxe2x80x9d or xe2x80x9cextraneous fumesxe2x80x9d is sometimes hereinafter used to encompass gases, vapors or fumes generated by a wide variety of liquid volatile or semi-volatile substances such as gasoline, kerosine, turpentine, alcohols, insect repellent, weed killer, solvents and the like as well as non-liquid substances such as propane, methane, butane and the like. Many inter-related factors influence whether a particular fuel spillage does lead to ignition. These factors include, among other things, the quantity, the nature and physical properties of the particular type of spilt fuel. Also influential is whether air currents in the room, either natural or artificially created, are sufficient to accelerate the spread of fumes, both laterally and in height, from the spillage point to an ignition point yet not so strong as to ventilate such fumes harmlessly, that is, such that air to fuel ratio ranges capable of enabling ignition are not reached given all the surrounding circumstances.
One surrounding circumstance is the relative density of the fumes. When a spilt liquid fuel spreads on a floor, normal evaporation occurs and fumes from the liquid form a mixture with the surrounding air that may, at some time and at some locations, be within the range that will ignite. For example, that range for common gasoline vapor is between 3% and 8% gasoline with air, for butane between 1% and 10%. Such mixtures form and spread by a combination of processes including natural diffusion, forced convection due to air current draughts and by gravitationally affected upward displacement of molecules of one less dense gas or vapor by those of another more dense. Most common fuels stored in households are, as used, either gases with densities relatively close to that of air (eg. propane and butane) or liquids which form fumes having a density close to that of air, (eg. gasoline, which may contain butane and pentane among other components is very typical of such a liquid fuel).
In reconstructions of accidental ignition situations, and when gas water heaters are sometimes suspected and which involved spilt fuels typically used around households, it is reported that the spillage is sometimes at floor level and, it is reasoned, that it spreads outwardly from the spill at first close to floor level. Without appreciable forced mixing, the air/fuel mixture would tend to be at its most flammable levels close to floor level for a longer period before it would slowly diffuse towards the ceiling of the room space. The principal reason for this observation is that the density of fumes typically involved is not greatly dissimilar to that of air. Combined with the tendency of ignitable concentrations of the fumes being at or near floor level is the fact that many gas appliances often have their source of ignition at or near that level.
The present invention aims to substantially lower the probability of ignition in typical fuel spillage circumstances.
The invention provides a gas water heater including a water container adapted to be heated by a gas burner; an enclosure surrounding the burner and the water container, the water heater being characterized by having at least one opening adapted to allow air for combustion or extraneous fumes to enter the enclosure without igniting flammable extraneous fumes outside of the enclosure.
Preferably the at least one opening includes an aperture which is covered by a flame trap, which prevents the burner igniting extraneous fumes outside of the enclosure; and an air inlet through which air for combustion purposes is drawn.
Preferably the opening is remote from the gas burner and includes a duct for passage of air to the burner.
Preferably the opening and the aperture are collocated or are a single item.
Preferably the at least one opening is covered by a flame trap.
Preferably the aperture is in the enclosure.
Preferably the aperture is positioned close to a lower end of the enclosure.
Preferably the aperture is positioned in a lower end of the enclosure.
Preferably the aperture is positioned below the burner.
Preferably the aperture is positioned to allow air and fumes outside of the water heater to enter into an air passage leading to the burner.
Preferably the aperture allows air and fumes to enter the lowest point of the air passage.
Preferably one of or a combination of: a light detection or sensitive device; a flame detecting or sensitive device; a temperature sensitive or detecting device; a heat detecting or sensitive device; and an oxygen depletion sensitive or detection device, is located in the water heater to detect flame from the fumes if they have been ignited inside the enclosure.
Preferably the at least one opening includes an air inlet which is not covered by a flame trap, the air inlet having its lowest opening at a height of not less than about 500 millimeters or about 20 inches or more from the bottom of the enclosure.
Preferably the at least one opening is located at or adjacent to the highest point of the enclosure, if the enclosure has a height of about 500 millimeters or greater, from the bottom of the enclosure.
Preferably a snorkel device is provided to extend the at least one opening to a height above the highest point of the enclosure.
Preferably the flame trap includes a heat resistant permeable material having high thermal capacity.
Preferably the flame trap includes a screen selected from either woven or knitted mesh.
Preferably the flame trap is made of metal.
Preferably the flame trap is made of one of: steel, stainless steel, copper and aluminum.
Preferably a lint trap is included to wholly cover the aperture and the flame trap.
Preferably the lint trap is formed by mesh placed in the path of lint or dust to travelling to the flame trap means.
Preferably the water heater includes a gas shut off means which shuts off the gas supply to the burner and or a pilot burner if the air and fumes are ignited after entering the enclosure.
Preferably the gas shut off means includes a heat sensitive means.
Preferably the gas shut off means includes a flame sensitive switch.
Preferably the gas shut off means includes an oxygen depletion sensitive means.
Preferably the enclosure comprises a separable jacket and base.
Preferably the flame trap is provided at or as part of the construction of joining areas of the base to the jacket, or the jacket to other component or the base to other component or at any location where the fumes could enter the enclosure.
Preferably the flame trap is inherent in or is formed by the joining areas including either only gaps or apertures of a size small enough to act as a flame trap.
Preferably the flame trap has been added to the joining area or is deliberately incorporated as part of the joining area.
Preferably the flame trap is a layer of metallic mesh cooperating with the joining area to achieve the flame quenching or arresting function.
Preferably the flame trap is inside of the water heater.
Preferably the gas shut off means includes a light detection means.
The invention further provides a water heater having a burner adapted to combust gas to heat a water container above the burner within an outer enclosure having an opening to admit air required to combust the gas; and including air and extraneous fume flow means co-operative with the opening to reduce or eliminate a possibility of extraneous fumes adjacent the enclosure being ignited outside the enclosure by a gas flame associated with the burner.
Preferably a fume detecting device is located in the water heater to detect fumes after they have entered the enclosure.
Preferably the at least one opening is positioned close to a lower end of the enclosure.
Preferably the at least one opening is positioned in a lower end of the enclosure.
Preferably the at least one opening is positioned below the burner.
Preferably the at least one opening is positioned so as to allow air and fumes outside of the water heater to enter into an air passage leading to the burner.
Preferably the at least one opening allows air and fumes to enter the lowest point of the air passage.
Preferably one of or a combination of: a light sensitive device; a flame detecting device; a temperature detecting device; a heat detecting device; and an oxygen depletion measurement device, is located in the water heater to detect flame from fumes after they have been ignited.
Preferably the flame trap is a flame quenching or arresting means.
Preferably the device or devices are included in a gas shut off device.
Preferably one of or a combination of: a light detection or sensitive device; a flame detecting or sensitive device; a temperature sensitive or detecting device; a heat detecting or sensitive device; and an oxygen depletion sensitive or detection device, is located in the water heater to detect flame from fumes if they have been ignited inside the enclosure.
Preferably device or devices are included in a gas shut off device.
The invention also provides a water heater having a burner adapted to combust gas to heat a water container above the burner within an outer enclosure having an opening to air required to combust the gas; and including air and extraneous fume flow means cooperative with the opening to reduce or eliminate a possibility of fumes adjacent the enclosure being ignited outside the enclosure by a gas flame associated with the burner; the water heater including gas shut off means which has a flame detecting or sensing device located in a path of flame external to a combustion chamber of the water heater and also located in any path of flame of fumes ignited in the enclosure.
Preferably the flame external to the combustion chamber is caused by flame spillage from the burner caused by a blockage of an exhaust flue.
Preferably the flame external to the combustion chamber is caused by air starvation in the combustion chamber.
One advantage of the invention is the provision of a barrier to the unprotected entry, at the lower end of the jacket or enclosure, of flammable extraneous fumes. In alternative embodiments it provides a protected entry means for such fumes near or at the base of the enclosure in which case these extraneous fumes are consumed in a controlled manner. The protected entry is, in the most preferred form, a flame trap preventing ignition of the remaining fumes in the surrounding atmosphere or of any liquid remaining nearby.
An advantage of locating the air intake for combustion purposes above the midpoint of the gas water system is that it reduces the chance of extraneous fumes entering the heater via the air intake because generally such flammables are heavier than air, which in the main do not attain dangerous levels at the air intake level.
The use of air close-off means and gas shut-off means activated by a trigger provides the advantage of suffocating any flame in the heater, or switching off the gas supply, or preventing uncontrolled or undirected ignition of gases or vapors from exiting the heater environment.
By providing an extended air intake, the risk of lint or dust affecting the efficiency of the water heater is reduced.